Your 11 year old is considered an adult on the dining plan, the 7 year old a child.
Depends on which plan you want.
Quick service plan (2 QS meals, 2 snacks per night, 1 resort mug, per person) is $29.99 per adult per night, $8.99 per child.
Regular dining plan (1 TS, 1 CS, 1 Snack per night, per person) $39.99/$10.99
Deluxe dining plan (3 meal credits, 2 snacks per night, 1 resort mug, per person) $71.99/$21.99